Soft Robotic Grippers Based on Particle Transmission

The actuation of soft robotics has relied predominantly on pneumatic or hydraulic transmissions. However, these transmissions require good sealing and complicated valve control systems. Robots based on such transmissions are also tethered to bulky pneumatic or hydraulic pumps. In many practical grasping applications, soft actuators are expected to show several-fold stiffness change, which is difficult to achieve in pneumatic or hydraulic soft actuators. In this paper, a novel particle transmission method is proposed for soft gripper design. In the proposed method, particles enclosed in an elastic membrane are driven by a piston, thus problems associated with sealing are resolved as long as particle diameter is greater than the clearance between the piston and the cylinder. By controlling the volume of particles injected into the elastic membrane, bending of the actuator is achieved and its stiffness is increased accordingly. In the experiments, when injected particle volume is changed from 1.0 to 1.8 times that of the actuator's initial volume, the actuator bends up to 60° and its stiffness is increased by nearly seven folds from its initial state. A sample soft robotic gripper made of three such soft actuators is developed to test the feasibility and capability of the proposed method. It is believed that the proposed method could provide an important alternative to soft robotic gripper design and development.